Development of a Brønsted acid Al–MIL-53 metal–organic framework catalyst and its application in [4 + 2] cycloadditions

Abstract

Two Al–MIL-53 derived metal–organic frameworks (MOFs) were developed to serve as efficient heterogeneous Brønsted acid catalysts. Sulfonic acid functional groups were successfully incorporated into the framework by post-synthetic modification (PSM) using commercially available reagents. The synthesized Al–MIL-53–RSO₃H and Al–MIL-53–ArSO₃H Brønsted acid–MOF catalysts were fully characterized by SEM, powder XRD, FTIR, TGA and N₂ adsorption/desorption isotherms. An efficient [4 + 2] cycloaddition of 2-vinyl-substituted phenols was evaluated using the newly synthesized Al–MIL-53–RSO₃H and Al–MIL-53–ArSO₃H catalysts. The Al–MIL-53–RSO₃H and Al–MIL-53–ArSO₃H catalysts were found to be compatible with a variety of substituted substrates; finally, they can be recycled five times without compromising the yield or selectivity of the reaction.